The present invention relates to a method for adjusting drilling of a drilling machine in a drilling machine comprising a frame, a percussion piston arranged to the frame and moving in the longitudinal direction of the frame, an absorber situated in the front end of the travel of the piston portion of the percussion piston, a shank situated in the axial extension of the percussion piston and at least two pistons arranged to the frame moveable in its axial direction, the pistons being situated in axial cylinder spaces formed around the shank and arranged to act on the shank and push it towards the front portion of the drilling machine by means of a pressure medium acting on the rear surface of the pistons, whereby at least during drilling such a pressure of pressure medium is set to act on the rear surface of the pistons that the total force of all the pistons acting on the shank and pushing it forwards exceeds feed force acting on the drilling machine during drilling, wherefore some of the pistons are pushed to the foremost position of their travel by means of the pressure medium, whereby the shank is at its optimal percussion point when being supported by them.
The present invention also relates to a drilling machine which drilling machine comprises a frame, a percussion piston arranged to the frame and moving in the longitudinal direction of the frame, an absorber situated in the front end of the travel of the piston portion of the percussion piston, a shank situated in the axial extension of the percussion piston, and an axial bearing arranged to the frame for receiving axial forces directed to the frame via the shank, which axial bearing is formed of at least two pistons which are placed in the frame into axial cylinder spaces formed around the shank and arranged to act on the shank and push it towards the front portion of the drilling machine by means of a pressure medium acting on the rear surface of the pistons, whereby at least during drilling such a pressure of pressure medium is set to act on the rear surface of the pistons that the total force of all the pistons acting on the shank and pushing it forwards exceeds the feed force acting on the drilling machine during drilling and whereby the travel of some of the pistons towards the front portion of the drilling machine is restricted in such a manner that when said pistons are in their foremost position, the shank is essentially situated at its optimal percussion point when being supported by them.
When drilling holes with a rock drill, drilling conditions vary in various ways and in some situations it is necessary to be able to adjust fast and effectively the percussion power of the rock drill or other factors having an effect on drilling. In prior art solutions, percussion power is adjusted by adjusting the pressure of the pressure fluid in the percussion machinery, which is, however, quite difficult to realize accurately and in a controlled manner. Further, in prior art solutions, the position of the shank with respect to the percussion piston is always to be kept at a certain so-called optimal percussion point where as great a portion of percussion power as possible moves to the shank and via the shank through the drill rod to the drill bit. Finnish Patent 84,701 discloses a solution where the position of the shank is set by using several pistons, the pressure acting on which together pushes the shank into an optimal percussion point, but allows it to move backwards by means of a strong return pulse and to receive thus the stress created. In said Finnish Patent some of the pistons can also move farther than the others towards the front end of the drilling machine and thus follow that shank, whereby they receive the return movement and absorb it at an earlier stage during the return pulse.